"David Robbins" wrote in message
...

"Andy Cowley" wrote in message
...
CW wrote:

Effective lightning protection can be done in the amateur station for
a
reasonable cost. Most though, don't do so.
"Andy Cowley" wrote in message
...

As I understand it, there is nothing that can work if
a direct lightening strike occurs.

How? How do you deal with thousands of amps? It's for certain sure that
a simple spark gap will be blown to kingdom come in the first
millisecond,
so what happens in the next millisecond? and the one after...........

I think your method must be untried, untested and 'whistling in the
dark'.

Andy, M1EBV

lightning doesn't go on for milliseconds, 50 micro-seconds is a relatively
long stroke. 30kA can go through a 12ga copper wire with no damage for
10-20 microseconds. in most cases there will actually be very little
voltage between wires of a coax or twin lead just because their insulation
will break down or the feedpoint of the antenna will arc over... both are
naturally occurring spark gaps that actually work very well to protect
equipment from direct strikes. assuming of course the tower and feedline
have good grounds. where people have problems is they don't ground the
shield of the coax to a single point ground along with the power lines, so
they get differential voltages between grounds that has no place to go but
through the equipment. properly grounded installations with relatively
small arresters to limit voltage on the center conductor of the coax
relative to the shield are very effective. for tube type receivers a
simple
spark gap is adequate, for transistorized stuff you may need lower voltage
protection and should probably get something commercially made for the
job.

I've seen a common spark plug used to provide a spark gap for antennas.
Setting the gap to about .05 inches will conduct much of the current away
from the down stream circuitry. Some have suggested a few turns of the
Coax after the gap will provide enough inductance to deter conduction past
the gap, but I haven't pursued that to establish it as fact. There is also
the problem of causing an impedance mismatch with an inductance in the line.
The gap being smaller than the spacing of the coax would seem to be enough
to minimize damage.